Analysis of thermal residual stress in a thick-walled ring of duralcan-base Al-SiC functionally graded material
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I.
INTRODUCTION
FUNCTIONALLY graded materials (FGMs) are conceptually new composite materials that have a tailored composition in a designed direction.[1] One of the promising FGM manufacturing methods is the centrifugal method, which is an application of the centrifugal casting technique and whose products are rings and tubes. The method uses the difference in centrifugal forces between molten metal and ceramic particles to form a graded composition along the radial direction.[2,3] Because of the composition gradient of FGMs, they also have macroscopically graded mechanical properties; e.g., Young’s modulus and the linear expansion coefficient in the radial direction. Thus, thermal misfit strains, and hence residual stresses, are inherently induced in FGM products when FGM rings and tubes are manufactured. In designing metal-ceramic FGMs as structural or component materials, the knowledge of the residual stress is important not only to prevent undesirable deformation and cracking, but also to ensure the high reliability of the products. The aim of the present study is to examine the macroscopic thermal residual stresses in Al-SiC FGM rings theoretically and experimentally. Machining Al-SiC FGM rings is known to be extremely difficult because of distributed SiC particles, and because the heat associated with the turning introduces other thermal residual stresses. Thus, for our experiment, we cannot adopt one of the well-established experimental techniques known as Sack’s method,[4] YASUYOSHI FUKUI, Professor, is with Department of Mechanical Engineering, Faculty of Engineering, Kagoshima University, Kagoshima 890, Japan. YOSHIMI WATANABE, Associate Professor, is with the Faculty of Textile Science & Technology, Shinshu University, Ueda 386, Japan. Manuscript submitted December 15, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS A
which needs the turning of a ring. Therefore, we shall adopt a simple and robust cutting method in which the deformation, after the ring is cut at one cross section, is measured, and then the initial stress state is determined by solving an inverse problem. Microscopic residual stress caused by a similar thermal misfit[5,6,7] is not considered here. In the following sections, we analyze the distribution of macroscopic thermal residual stresses in Al-SiC FGM rings. Functionally graded material rings with rectangular cross sections and the composition gradient in the radial direction were investigated. We present the Al-SiC FGM-ring manufacturing method first. An effort was also spent to develop a theoretical model based on the theory of elasticity,[8–11] considering the graded mechanical properties. A ring diametral compression test was also performed to validate the analysis. II.
EXPERIMENT
A. Material and Specimen Material used in the present study is Duralcan F3D.20S (20 vol pct SiC-Al alloy composite) ingot (delivered from Alcan Asia Limited, Chiyoda-ku Tokyo, Japan), because it can simplify the procedure of obtaining homogeneous metal—ceramic master composite material. A vertical c
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